1. Graduate Research Assistant, Dept. of Civil and Environmental Engineering, Yonsei Univ., Seoul 120-749, Republic of Korea.
2. Postdoctoral Research Fellow, Dept. of Civil and Environmental Engineering, Yonsei Univ., Seoul 120-749, Republic of Korea.
3. Associate Professor, Dept. of Civil and Environmental Engineering, Yonsei Univ., Seoul 120-749, Republic of Korea (corresponding author).